The _ catch-all branch does not set up lexeme correctly

I.e.:

# let lexbuf = Sedlexing.Utf8.from_string "x";;
val lexbuf : Sedlexing.lexbuf = <abstr>
# match%sedlex lexbuf with _ -> Sedlexing.Utf8.lexeme lexbuf;;
# print_endline (match%sedlex lexbuf with _ -> Sedlexing.Utf8.lexeme lexbuf);;

Expected output: x.